In two and four-wire data and telecommunications networks, various types of attenuating devices in modular form are conventionally used to control signal amplitude levels as the signal feeds through the network. The device is usually designed to be adjustable to provide variable attenuation or gain adjustment because the loss in signal amplitude typically depends upon the length of the electrical conductor or cable to which the device is connected. The lengths of such lines may vary from one installation to another. In addition, the impedance of the line which causes signal loss may vary depending upon the particular condition of the line transmitting the signals.
A variety of conventional signal attenuating devices of an analog-type are used to effect the necessary changes in the amplitude of the signal. Such devices include single turn and multiple turn variable resistors or potentiometers embodying one or more precision resistors which can be tapped off by movement of a linear slider or rotary wiper arm to apply more or less resistance to the circuit, thereby correspondingly varying the signal loss or gain. For use in data and telecommunications circuits, the variable resistor is typically designed to apply up to 16 decibels of loss to the signal in the circuit.
More recently, the trend in the art is to provide level adjustment by means of incrementally controlled switches which adjust the gain or loss in a digital manner using some binary-based numerical sequence to provide the desired decibel range and resolution.
For data and telecommunications circuit applications, the attenuator should provide the desired signal attenuation with the requisite resolution. Preferably, the attenuator should also have the capability of providing an output signal which is exactly equal to the input to which the attenuator is connected. Thus, if the attenuator can be set to provide a gain of unity to signals from any data or telecommunications circuit to which the attenuator is connected by monitoring the output of the attenuator, the level of the signal inputted to the attenuator can be extrapolated because it is essentially an exact replica of the output signal. This allows an installer coupling into a telecommunications circuit of unknown characteristics to determine, by simply measuring the output signal level of the attenuator, if the signal output of the circuit to which the attenuator is connected is at a particular level. This feature is especially important if it is difficult to obtain direct access to the internal terminals of the circuit to monitor the levels of the signals transmitted by such circuit. This capability is also important to provide precise alignment in signal levels between the signals of the two circuits respectively coupled to the input and output terminals of the attenuator circuit.